1. Field of the Invention
The present invention relates to a servo amplifier for use in a controller for various industrial machinery such as a machine tool, a robot, an injection molding machine, a wire electric discharge machine and an electrical press machine.
2. Description of the Related Art
FIG. 7 illustrates a circuitry structure of a servo amplifier generally known in the art. An alternating current from a three-phase alternating-current power supply 1 is converted to a direct current by a semiconductor module 2 constituted by a rectifier circuit such as a diode bridge circuit, and then smoothed by an electrolytic capacitor 3. Subsequently, the direct current is converted into a desired alternating current under PWM control by a semiconductor module 4 and a control circuit 5 which constitute an inverter circuit, so as to drive control a servomotor 6. In FIG. 7, a circuit A 7 includes a charging circuit for gradually charging the electrolytic capacitor 3 when the power supply is turned on, a circuit B 8 includes a direct-current voltage detection circuit and a dynamic braking circuit for absorbing a regenerative current, a circuit C 9 includes a current detection circuit, and a circuit D 10 includes circuits for dynamic braking and for detecting electric current.
A general servo amplifier is constituted by parts or components shown in FIG. 7 except the three-phase power supply 1 and the servomotor 6, that is, the semiconductor modules 2 and 4, the control circuit 5, the electrolytic capacitor 3 and the circuits 7 to 10. In some servo amplifiers, the semiconductor module 2 constituting a rectifier circuit is not accommodated in the same unit case which contains the other parts or components. In the servo amplifier described above, the semiconductor modules 2 and 4 are components which mainly generate heat, although the circuits 7-10 include heat generating parts.
FIG. 4 is a diagram of the amplifier having the above-described servo amplifier circuitry as viewed from the bottom of the amplifier for showing the internal arrangement thereof.
The aforementioned parts or components constituting the servo amplifier are separately mounted on two printed circuit boards 11 and 12 which are arranged opposite to each other. One or both of the semiconductor modules 4 and 2 are mounted on the printed circuit board 11 or 12 so that heat radiating surfaces 4a and 2a thereof are parallel to the printed circuit board 11, 12. In the example shown in FIG. 4, one or both of the semiconductor modules are mounted on the printed circuit board 11. The heat radiating surface 4a, 2a of the semiconductor module 4, 2 has a large area for enhancing heat radiation, but since the heat radiating surface 4a, 2a extends parallel to the printed circuit board 11, 12, the size of the heat radiating surface 4a, 2a does not affect width of the servo amplifier, thus permitting reduction in the width of the amplifier. A flat heat pipe 23 is attached to the heat radiating surface 4a, 2a of the semiconductor module 4, 2, and a heat sink 24 is attached to a portion of the flat heat pipe 23 which is exposed outside from the rear of a unit case 20. This arrangement permits heat generated by the semiconductor module 4, 2 to be conducted to the heat sink 24 and radiated therefrom away from a region in the unit case 20 where the other components are disposed.
The heat sink 24 is produced by die casting or the like as a one-piece structure including a flange 21 for mounting the servo amplifier on a locker or a casing of a controller. The length of the heat sink 24 in the width direction of the unit case 20 is smaller than the width of the unit case 20. Namely, the heat sink 24 is formed such that the width thereof is smaller than the width of the unit case 20. The unit case 20 is provided for preventing electric shock, supporting the printed circuit boards 11 and 12, and improving external appearance, and is securely fixed to the flange 21. In FIG. 4, reference numeral 22 denotes a terminal of the semiconductor module 4, 2.
In conventional servo amplifiers, the width of the amplifier is restricted by height of tall components among components 13 other than the semiconductor module 2, 4, which is for example a relay or an electrolytic capacitor 3, and other components of small height are mounted in spaces not interfering with such tall components. As a result, the width of the servo amplifier is determined by the height of the tallest component among the components mounted on the printed circuit boards 11 and 12.
Further, heat generated by the semiconductor module 4, 2 is radiated from the heat pipe 23 and the heat sink 24, to cool the module 4, 2, but there are some other components of the servo amplifier in the unit case 20 which generate considerable heat and need to be cooled. To cool such components, a fan motor is provided in the amplifier to carry out forced air cooling.
On the other hand, there is requirement of downsizing of apparatus into which the servo amplifier is incorporated, and thus the servo amplifier is desired to be downsized. To downsize the servo amplifier, it is the best way to make the amplifier thinner by reducing its width, in view of mounting compatibility with existing types and also matching in shape with other types. However, if the servo amplifier and thus the unit case thereof are reduced in size, the components of the servo amplifier are densely arranged within the unit case, and heat generating components contained in the unit case need to be cooled with higher efficiency since heat generated by the components adversely affects the other surrounding components.